Successfully reported this slideshow.
We use your LinkedIn profile and activity data to personalize ads and to show you more relevant ads. You can change your ad preferences anytime.

Introduction to Message-Oriented Middleware


Published on

A talk given to the University of Limerick in 2005 on Message-Oriented Middleware

Published in: Technology

Introduction to Message-Oriented Middleware

  1. 1. Introduction toMessage-Oriented Middleware Invited Talk to University of Limerick February ‘05 Edward Curry National University of Ireland, Galway
  2. 2. Further InformationMessage-Oriented Middleware in Middleware for Communications, Q. H. Mahmoud, Ed. Chichester, England: John Wiley and Sons, 2004, pp. 1-28. Full text available at:
  3. 3. Presentation Outline Interaction Models – Synchronous & Asynchronous Communication Introduction to the Remote Procedure Call (RPC) Introduction to Message-Oriented Middleware (MOM) – When to use MOM or RPC MOM Overview – Message Queues – Messaging Models • Point-to-Point & Publish/Subscribe • Comparison of Messaging Models Service-Oriented Architectures – Role of XML, Web Services, SOAP, MOM – Developing Service-Oriented Architectures Introduction to Message-Oriented Middleware 3
  4. 4. Challenges of Distributed ComputingDirect Remote Procedure Call (RPC) mechanisms struggle in large-scale widely distributed deploymentsAlternative to RPC has emergedMessage-Oriented Middleware –any middleware infrastructure providing messaging capab. –peer-to-peer relationship between individual clients –each peer can send/receive messages to/from other peers Introduction to Message-Oriented Middleware 4
  5. 5. Interaction Models Two model dominate distributed computing environments – synchronous and asynchronous communication – a solid knowledge of models is key to understanding benefits and differences between MOM and other forms of distribution Synchronous Interaction – caller must block & wait (suspend processing) until the called completes – participants do not have processing control independence • they rely on the return of control from the called systems Asynchronous Interaction – caller retains processing control, does not need to block – requires an intermediary to handle the exchange of requests – participants retain processing independence (continue processing) regardless of the state of the others Introduction to Message-Oriented Middleware 5
  6. 6. Synchronous Communication Introduction to Message-Oriented Middleware 6
  7. 7. Asynchronous Communication Introduction to Message-Oriented Middleware 7
  8. 8. Introducing RPC Traditional Distribution model – Utilized in middleware platforms including • CORBA, Java RMI, Microsoft DCOM & XML-RPC – Based on the synchronous interaction model RPC creates a facade, making both processes believe they are in the same process space – Similar to a local procedure call • control is passed to procedure in sequential synchronous manner Direct conversation between two parties – (similar to a person-to-person telephone conversation) Introduction to Message-Oriented Middleware 8
  9. 9. RPC DeploymentIntroduction to Message-Oriented Middleware 9
  10. 10. RPC Cont. Coupling – invasive mechanism of distribution – works on object or function interfaces, producing tightly coupled systems – Inflexible method of integrating multiple systems Reliability – most impl. provide little or no guaranteed reliable communication capability – very vulnerable to service outages Scalability – blocking nature of RPC can adversely affect performance – subsystems do not scale equally, effectively slows whole system down to the maximum speed of slowest participant – synchronous interactions use more bandwidth (several calls are needed) Availability – systems built using the RPC model are interdependent – require simultaneous availability of all subsystems Introduction to Message-Oriented Middleware 10
  11. 11. MOM Based on the asynchronous interaction model – not required to block and wait on a message send Allows delivery of messages when the sender or receiver is – not active or available to respond at the time of execution Supports delivery for messages that may take minutes to deliver – as apposed to RPC that delivers in milliseconds or seconds • ( ! 100% True) Sending application has no guarantee message will be read nor is it given guarantee about the time it will take to deliver – these aspects are mainly determined by the receiving application Similar to the postal service – Messages are delivered to the post office; the postal service then takes responsibility for safe delivery of the message Introduction to Message-Oriented Middleware 11
  12. 12. MOM DeploymentIntroduction to Message-Oriented Middleware 12
  13. 13. MOM Coupling – creates loose coupling between participants in a system • independent layer acts as an intermediary to exchange messages • ability to link systems without adapting source and target systems Reliability – guarantee message delivery to each intended recipient exactly once • message loss is prevented by using a store and forward mechanism – high-level of reliability (typically configurable) Scalability – decouples performance characteristics of the subsystems from each other • subsystems can scale independently – messaging models contain natural traits for effective load balancing (…) Availability – high availability capabilities – does not require simultaneous or “same-time” availability of all subsystems Introduction to Message-Oriented Middleware 13
  14. 14. When to use RPC or MOM RPC – suffers from inflexibility and tight coupling – problematic to scale parts of the system and deal with service outages – assumes simultaneously available – require more bandwidth than a similar MOM interaction – designed on the notion of a single client talking to a single server, traditional RPC has no built in support for one-to-many communications – simplicity of the mechanism and straightforward implementation – guarantee of sequential processing - RPC is slow but consistent • work is always carried out in the correct order. • important considerations for systems that requires 100% temporal integrity – temporal inaccuracies RPC is ideal if you want a strongly-typed/OO system with tight coupling, compile-time semantic checking and more straightforward impl. MOM is an ideal solution if the systems will be a geographically dispersed deployment with poor network connectivity and stringent demands in reliability, flexibility and scalability Introduction to Message-Oriented Middleware 14
  15. 15. Overview MOM MOM Overview – Message Queues – Messaging Models • Point-to-Point & Publish/Subscribe • Comparison of Messaging Models Introduction to Message-Oriented Middleware 15
  16. 16. Message Queues Queues provide ability to store messages on MOM Queue are sorted in a particular order – standard queue is the First-In First-Out (FIFO) queue Other Types of Queues – Public Queue – Private Queue – Temporary Queue – Journal Queues – Connector/Bridge Queue – Dead-Letter/Dead-Message Queue Introduction to Message-Oriented Middleware 16
  17. 17. Message QueuesIntroduction to Message-Oriented Middleware 17
  18. 18. Messaging Models Two main message models are commonly available – point-to-point – publish/subscribe Both are based on the exchange of messages through a channel (queue) Typical system will utilize a mix of these models to achieve different messaging objectives Introduction to Message-Oriented Middleware 18
  19. 19. Point-to-Point Model Straightforward asynchronous exchange of messages – message routed to consuming clients via a queue – no restriction on number of publishing clients – usually only a single consuming client (not a strict requirement) • each message is delivered only once to only one receiver Messages are always delivered and will be stored in the queue until a consumer is ready to retrieve them Introduction to Message-Oriented Middleware 19
  20. 20. Publish Subscribe Models One-to-many and many-to-many distribution mechanism – allows single producer to send a message to one user or potentially hundreds of thousands of consumers Clients "publish" to a specific topic or channel Channels are “subscribed” to by clients to consume msgs No restriction on the role of a client – may be both a producer and consumer of a channel§ Introduction to Message-Oriented Middleware 20
  21. 21. Hierarchical Channels Hierarchical channels (topics) – Destination grouping mechanism in pub/sub model – Structure allows channels to be defined in a hierarchical fashion – Each sub-channel offers a more granular selection of the messages contained in its parent – Clients subscribe to the most appropriate level of channel  In large-scale systems, grouping of messages into related types (i.e. into channels) helps to manage large volumes of different messagesIntroduction to Message-Oriented Middleware 21
  22. 22. Comparsion of ModelsMost messaging objectives can be achieved using either model or combination of bothFundamental difference – publish/subscribe model • every consumer to a topic/channel will receive a message published to it – point-to-point model • only one consumer will receive itTopics can be used to categorize different types of messagesPub/Sub model is more powerful messaging model for flexibility, but it is more complex Introduction to Message-Oriented Middleware 22
  23. 23. MOM ServicesMessage FilteringTransactionsReliable Message DeliveryGuaranteed Message DeliveryMessage FormatsLoad BalancingClustering Introduction to Message-Oriented Middleware 23
  24. 24. Programming MOM A large number of MOM implementations exist – WebSphere MQ (formerly MQSeries), TIBCO, SonicMQ, Hermes, SIENA, Gryphon, JEDI, REBECCA, OpenJMS, etc Java Message Service (JMS) – Common way for Java programs to create, send, receive and read MOM messages – JMS specification defines • general purpose Application Programming Interface (API) • set of semantics that describe the interface and general behaviour of a messaging service Write code once using API and plug-in desired MOM – makes client-messaging code portable between MOM providers Introduction to Message-Oriented Middleware 24
  25. 25. Service Oriented Architecture The problems and obstacles encountered during system integration pose major challenges for IT departments: “70% of the average IT department budget is devoted to data integration projects” –IDC “PowerPoint engineers make integration look easy with lovely cones and colorful boxes” – Sean McGrath, CTO, Propylon“A typical enterprise will devote 35% - 40% of its programmingbudget to programs whose purpose is solely to transferinformation between different databases and legacy systems”-Gartner Group Introduction to Message-Oriented Middleware 25
  26. 26. Service Oriented Architecture MOM used to create highly open and flexible systems that allow the seamless integration of subsystems MOM solves many of the transport issues with integration However, major problems still exist with the representation of data, its format and structure To develop a truly open system, MOM requires the assistance of additional technologies such as XML and Web Services Introduction to Message-Oriented Middleware 26
  27. 27. XML Programming language and platform independent format for representing data – eliminates any networking, operating system or platform binding that a binary proprietary protocol would use Once data is expressed in XML, it is trivial to change the format To use XML as a message exchange medium, standard formats need to be defined to structure the XML messages – i.e. ebXML andOASIS Universal Business Language (UBL) • With UBL, you convert your internal message formats to the standard UBL format and export to the external environment Introduction to Message-Oriented Middleware 27
  28. 28. Web Services Web Services – platform and language independent standards defining protocols for heterogeneous integration Can be seen in a number of ways – Business-to-business/enterprise application integration tool – natural evolution of basic RPC mechanism A key benefit of a web services deployment is that they act as a facade to the underlying language or platform Web services which are often touted as a replacement for traditional RPC – Viewed in this light they still suffer from many of its shortcomings Introduction to Message-Oriented Middleware 28
  29. 29. SOAPThe Simple Object Access Protocol (SOAP) – simple and lightweight mechanism for exchanging structured and typed information between peers in a decentralized, distributed environment using XML – allows you to bind it to a transport mechanism • SMTP, HTTP, or JMSHas a number of uses – document exchange protocol – heterogeneous interoperability standard – wire protocol standard (something not defined in JMS) – RPC mechanismIn this talk we SOAP see as a document exchange protocol between heterogeneous systems Introduction to Message-Oriented Middleware 29
  30. 30. Developing SOAsThrough a combination of XML, SOAP and WS, we are able to create Service-Oriented Architectures (SOA)A service is a set of input messages sent to a single or composition of objects, with the return of causally related output messages –fundamental design concept is to reduce processing to logic black boxes –standard XML format for input and output formatsAn important aspect of SOAs is message centric structureOnce initial infrastructure created for the architecture, the amount of effort to connect to further systems is minimal Introduction to Message-Oriented Middleware 30
  31. 31. XML Transformation Pipelines Where message formats differ – XML based integration can convert the message to and from the format using XML transformation pipeline – data transformation can be seen as just another assembly line problem – with transformations taking place outside of the applications it a non-invasive method of integration Introduction to Message-Oriented Middleware 31
  32. 32. Sample SOA DeploymentIntroduction to Message-Oriented Middleware 32
  33. 33. SOA SummaryXML + Web Services + MOM = Open SystemsService Oriented Architecture Introduction to Message-Oriented Middleware 33
  34. 34. SummaryAll good Distributed Application Deployments (DAD)s need a good Message-Oriented Middleware (MOM) -Anon. Introduction to Message-Oriented Middleware 34